Human speech consists of complex sounds of an involved pattern. To be able to speak, it is not enough to have good hearing. To a baby in its first months speech is nothing more than a kind of a noise. To master speech, a child must learn to single out from a flow of sounds the essential features, or the phonemes. What one needs to perceive speech is not so much a keen ear as an ear trained to the system of a particular language.

If you do not know a foreign language, you will not be able to distinguish the individual elements of that language in the flow of sounds. You will not be able to repeat the words and phrases you hear, let alone understand them.

It is an interesting and important fact that this process is performed not merely by the acoustic regions of the brain, but also by the articulatory organs, which take part in the utterance of speech sounds, and by the corresponding motor regions of the brain. Even adults, although they usually do not realize it, do not perceive speech eiiher by sounds or visual appearance (written text), but by so-called kinaesthetic perception, a vague, inner sensation arising in the muscles and tendons of the articulatory organs during speech.

Acoustic information is analyzed in the temporal lobes of the cerebral cortex. Like all the other analysers in the human brain, the temporal lobes of the cortex consist of the primary or projection zones, to which the nerve fibres from each ear come, and the secondary zones which receive information not from the periphery, but that already processed by the primary zones.

If the primary zones have been affected by disease, the patient will have hearing trouble. It is quite a different matter if the secondary zone of the left hemisphere is damaged. The hearing is practically intact, but speech hearing is gravely affected. They cannot distinguish d from t, b from p and z from s. Obviously, they fail to identify phonemes and consequently have difficulties in understanding words.